Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
Contact etch stop layers are used to ensure that electrical contacts form in the proper layer(s) of image sensor device architecture. They allow for precision manipulation of etch rate as well as controlled stoppage on critical device structures. Stress induced by contact etch stop layers has also been shown to boost transistor drivability and enhance image sensor performance.
However, the use of contact etch stop layers is not without its drawbacks. Their inherent positive charge can reduce silicon surface hole concentration and increase dark current among integrated circuit devices. Additionally, the stress induced by contact etch stop layers can cause silicon lattice distortion and result in circuit noise.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.